1,720,979 research outputs found
Large scale soil-foundation-structure model in Greece: Dynamic tests vs FEM simulation
No full textThis paper provides the results of FEM simulation of dynamic tests recently performed in Thessaloniki on a large-scale single-degree-of-freedom structure resting on a soft soil. The structure (named EuroProteas) was specifically designed to mobilize strong soil-structure interaction (SSI), being a particularly stiff structure founded on soft soil. It consists of a simple steel frame with removable X-bracings founded on a RC slab and supporting the superstructure mass of two RC slabs identical to the foundation slab. It is a totally symmetric structure. Subsoil stratigraphy and dynamic properties of the foundation soil are derived from extended geotechnical and geophysical surveys, including static and dynamic in-situ and laboratory tests. Extensive free- and forced-vibration tests were performed. This paper deals with one set of forced-vibration tests. An eccentric mass shaker was used as a source of harmonic excitation (finput = 3, 4.5, 5, 7 Hz and eccentricity 6.93kg-m) imposed on the roof of the structure. The structural response is recorded by seven accelerometers, five of which are located at the top of the roof slab and two at the top of the foundation slab. Soil response is recorded with seismometers installed on the free soil surface in both horizontal directions. Dynamic FEM modelling of the tests were conducted in the time and frequency domains in order to detect the main aspects of SSI, taking into account soil nonlinearity. Numerical and experimental results were extensively compared. Very interesting results were reached above all in terms of the effects of soil-foundation interface behaviour
Frequency vs time domain analysis for the calculation of foundation stiffness and damping.
No full textFunzioni di impedenza per fondazioni superficiali: esperienze dal progetto SISIFO
No full textQuesto articolo presenta e discute i risultati ottenuti nell’ambito del progetto di ricerca SISIFO volto a calcolare le funzioni di impedenza di una fondazione superficiale dalle registrazioni del comportamento dinamico del prototipo in scala reale di oscillatore semplice su fondazioni superficiali EuroProteas. Il prototipo è collocato presso il sito strumentato Euroseistest in Grecia su alternanze di argilla e sabbia deformabili, la cui rigidezza si riduce a pochi metri di profondità . A tal fine, sono state eseguite prove di rumore ambientale, vibrazioni libere e forzate in un'ampia gamma di frequenze e ampiezze di interesse per l'ingegneria sismica. Le funzioni di impedenza sperimentali sono state poi confrontate e validate con le soluzioni analitiche maggiormente utilizzate in letteratura. Infine, è stato realizzato un modello numerico attraverso il software SAP2000 in cui la deformabilità del terreno di fondazione è stata introdotta mediante molle elastiche, la cui rigidezza è stata calibrata considerando sia le impedenze analitiche che sperimentali. La frequenza fondamentale ottenuta dall’analisi modale del modello la cui interazione con il terreno di fondazione è stata definita a partire dalle impedenze sperimentali riproduce la frequenza sperimentale meglio di quello in cui le molle sono calibrate con le funzioni analitiche. Tali risultati mostrano dunque l'efficacia dell'utilizzo di funzioni di impedenza sperimentali nelle simulazioni numeriche, soprattutto quando i parametri equivalenti del terreno risultano difficili da definire, come nel caso in esame
Vulnerability assessment of Hassan Bey’s Mansion in Rhodes
No full textThe paper presents the vulnerability assessment of the Hassan Bey’s Mansion, located in the Medieval City of Rhodes in Greece. To this aim, the procedure developed in PERPETUATE project for the seismic assessment at scale of a single monument is adopted: it follows the performance – based concept making use of nonlinear static analyses. The main outcome of the assessment is presented in the paper in terms of maximum seismic intensity measure (the one selected as the most representative for the examined asset) compatible to various performance levels: it is used to address also the rehabilitation decisions. Within this context, the attention of this paper is focused on the use of sensitivity analysis for the identification of the main parameters that affect the structural response. Uncertainties considered in this application are both aleatory and epistemic. The epistemic uncertainties concern the effectiveness of the infilled openings: in fact, this feature strongly characterizes this building that has been subjected to many transformations along its life. Moreover, seven random variables have been considered to account for the aleatory uncertainties: they involve the material properties, the material constitutive law as well as floor rigidity. A total of 60 nonlinear static analyses have been performed for the sensitivity analysis, which represents a powerful tool for setting-up a possible investigation plan and addresses the final assessment. The resulting safety factor, computed in terms of return period, varies from 0.20 to 0.27, highlighting that the structure is not able to satisfy the target performance levels. Possible rehabilitation measures are proposed afterwards, in particular by quantitavely assessing the effect associated to the stiffening of diaphragms (very flexible in the original state)
On the effectiveness of experimentally-derived foundation impedance functions
No full textIn the past decades, several experimental and analytical investigations showed that the dynamic behavior of buildings can be significantly affected by the interaction with a soft foundation soil. In such cases, the actual response of structures founded on shallow foundations can be successfully simulated if the structural model is equipped with springs and dashpots calibrated through frequency-dependent impedance functions. This paper discusses the results of a research project aimed at back-calculating the impedance functions of a shallow square foundation from records of the dynamic behavior of the EuroProteas soil-foundation-structure (SFS) facility, deployed at Euroseistest (Greece). To this aim, forced-vibration tests were executed under different frequencies and increasing loading amplitudes. The experimental impedances were compared with several analytical solutions available in the literature, accounting for different hypotheses on the subsoil model. This comparison improved when the shear wave velocity VS used to define the analytical functions was reduced accounting for the strain level mobilized by the increasing amplitude of the applied force. A numerical model was realized in the SAP2000 software. The compliance of foundation soil has been introduced using elastic springs, the stiffness of which was calibrated considering either the analytical or the experimental impedances. The fundamental frequency obtained from a modal analysis of the SAP2000 model equipped with the springs calibrated on the experimental impedances turned out to reproduce the fundamental frequency of EuroProteas effectively measured on-site. Such results showed the effectiveness of using experimental impedance functions in the numerical simulations, especially when equivalent soil parameters are hard to define
Foundation impedance functions from full-scale soil-structure interaction tests
No full textThe paper presents and discusses the dynamic foundation impedance functions calculated from full-scale field
tests on soil-structure interaction at the prototype facility of EuroProteas at Euroseistest in Greece. The experimental campaign included ambient noise, free- and forced-vibration tests throughout a wide frequency and
amplitude range. The response of the soil-structure system was observed to be dominated by rocking. Hence, the
impedances were derived under two hypotheses, i.e. considering or neglecting the foundation swaying in the
dynamic equilibrium of the soil-structure system. The trend of the back-calculated impedance at high frequencies
was observed to vary depending on the interpretation model and turned out to be in satisfying agreement with
the available analytical solutions. Conversely, values at resonance were found almost independent of the test
type and of the interpretation model. These findings imply that i) the currently widespread non-destructive tests
(for instance ambient noise tests) can be effectively used to derive impedance functions; ii) the uncertainties are
minimized for the resonance frequency traditionally used to calibrate the flexible-base models for soil-structure
interaction analyses
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Medium-scale resonant wave barrier for seismic surface waves
Full text linkIn this work, we design an experimental campaign to assess the attenuation performance of a medium-scale resonant wave barrier operating within the frequency range of 50–100 Hz. In particular, the dispersive properties of (i) bare soil, (ii) a configuration of “dead masses” placed over the soil surface, and (iii) a locally resonant barrier, also known as metabarrier, are compared numerically. The resonant barrier introduces a significant amplitude reduction of the surface waves in a narrow frequency range around the resonant frequency of the resonators. Multiple-frequency barriers are designed with increasing and decreasing resonant frequencies to enlarge the attenuation frequency band
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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